Alkaline soil, also referred to as “sweet soil” by some gardeners, is identified as having a potential of hydrogen (pH) level above 7.0. A pH of 7.0 is considered neutral, and anything above is considered alkaline, or basic. Soil that is alkaline usually contains large amounts of calcium, sodium, and magnesium, and it is less soluble than acidic soil.

Plant growth is often reduced in alkaline soil because water and essential nutrients aren’t able to easily penetrate the soil. This can lead to nutrient deficiency and stunted growth in plants. Soil that is only slightly alkaline may be beneficial to some plants, such as lilacs and asparagus, but an overabundance of alkalinity is almost always detrimental to growth. In highly alkaline soils, iron, manganese, and phosphorus are not available in quantities high enough to sustain growth in most plants.

Alkaline soil commonly occurs in arid or desert regions with light rainfall, while areas that are heavily forested and have high rainfall tend to be more acidic. Regions that receive less than 20 inches (50 centimeters) of rainfall per year are most likely to have soil that is naturally alkaline. Watering soil with hard water that contains large amounts of lime will increase its alkalinity.

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Adding sulfur can make soil more acidic. Approximately 1 to 3 ounces (30 to 85 grams) of ground rock sulfur can be added per 1 square yard (or one square meter) of soil to raise the pH by 1.0 point. Less sulfur should be used for sandy soil, and more for clay soil, and it should be mixed in thoroughly before any planting is done. Adding organic matter such as sawdust, peatmoss, compost, and wood chips will also lower the soil's pH.

If lowering the pH of alkaline soil is not practical, or isn’t working, raised beds may be constructed, or topsoil may be used. There are many plants that can be grown in soil that's somewhat alkaline, and a garden of such plants isn’t unrealistic. Some plants that do well in this soil include oregano, oleander, cucumber, celery, mullein, and eucalyptus. Aloe, gardenia, lavender, chrysanthemum, iris, and zinnia also do well.

Testing for soil pH can be performed relatively inexpensively by a commercial soil testing laboratory. The county extension office in your area can provide information on gathering soil samples and submitting them for analysis. Home soil testing kits are also available from hardware stores and home and garden shops. Gardeners who suspect that under-performing plants are a result of the soil can test the soil for alkalinity and then work to amend the problem.

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Discuss this Article

anon327938Post 9

I need more information on field and Horticulture crops which can be grown under alkalinity of 7.5 pH to 9 pH.

shell4lifePost 8

@DylanB – Scientists have debunked that idea, but I tend to disagree with them. I have seen improvement in my flowers after adding pine needles to the soil around them, and these were flowers that wanted an acidic soil.

Pine needles are acidic, and it seems that when water runs over them and down into the dirt, the dirt should become more acidic. Maybe this isn't a scientific fact, but it makes sense to me, and since my flowers have become so much happier, I believe it.

Either way, the needles couldn't hurt. Even if all they do is make more nutrients available to the plants by keeping weeds down, it's worth the effort of spreading them around your plants.

DylanBPost 7

@JackWhack – I like growing chrysanthemums in my garden. My soil is alkaline and won't support just any plant.

Chrysanthemums don't smell great, but they are beautiful. Also, they bloom from late spring until frost, so you will get flowers from them long after most blooming plants have died.

At times, I've wished for my soil to be more acidic so that I could grow a bigger variety of plants. I don't have a compost pile or peat moss, but there is a pine forest nearby. Would pine needles work to make the soil more acidic?

JackWhackPost 6

Gardenias smell wonderful. I have alkaline soil near my house, so I planted a couple of gardenias next to the porch. Every time I walk up the steps, I can smell their sweetness.

What are some other shrubs for alkaline soil? I like planting shrubs instead of flowers from seed, because they are easier to take care of and not very picky.

PerdidoPost 5

Zinnias certainly aren't picky about soil. I've grown them in alkaline, acidic, and even extremely rocky soil, and they have flourished.

They have a shallow root system, but they are super sturdy. My dogs have walked across them and have even lain down on top of them without damaging them.

All they need is a little dirt, and they don't care about the pH. Since many of my other flowers do prefer acidic soil, I plant the zinnias in the alkaline soil.

FioritePost 3

@ Istria- You can also keep doctoring your soil instead of paying lots of money for professional analysis and new water systems. It might be easier to fertilize your garden area with compost, composted manure, or peat moss as well as planting a few plants that prefer soil that is more alkaline. Any of those three soil additives will increase the acidity of your soil, and adding a few plants will add variety to your garden.

GiraffeEarsPost 2

@ Istria- Before you go out and spend a bunch of money on water softeners, filters, etc, you should have a professional come and perform a soil analysis to determine the exact problem and cause of your soil issues. Once this is done, they can probably help you determine the best solution to mitigating your alkalinity problem.

istriaPost 1

This article was very helpful. I have alkaline soil, and it seems like nothing will fix it permanently. I live in an area that gets a decent amount of rain, so I would think that my soil would be acidic if anything. After reading this article, I found that maybe my soil is too alkaline because of the minerals in my water. How does lime get in my water, and is there any way that I can reverse this so that my water does not keep affecting my soil? My garden is small and I water it with my garden hose and a portable sprinkler, so it's not a huge area.

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